Garmin GMA 340 User manual

(GMA 340 and GMA 340 Dual ADF Shown)
£
Garmin International, Inc.
1200 E. 151st Street
Olathe, KS 66062 USA
190-00149-01 Revision L
June 2003
GMA 340 AUDIO PANEL
INSTALLATION MANUAL
(GMA 340, GMA 340H,
GMA 340 DUAL ADF)

Page A GMA 340 Installation Manual
Rev. L 190-00149-01
© Copyright 2003
Garmin Ltd. or its subsidiaries
All Rights Reserved
Except as expressly provided herein, no part of this manual may be reproduced, copied, transmitted,
disseminated, downloaded or stored in any storage medium, for any purpose without the express prior
written consent of Garmin. Garmin hereby grants permission to download a single copy of this manual and
of any revision to this manual onto a hard drive or other electronic storage medium to be viewed and to
print one copy of this manual or of any revision hereto, provided that such electronic or printed copy of
this manual or revision must contain the complete text of this copyright notice and provided further that
any unauthorized commercial distribution of this manual or any revision hereto is strictly prohibited.
Information in this document is subject to change without notice. Visit the Garmin web site
(www.garmin.com) for current updates and supplemental information concerning the operation of this and
other Garmin products.
Garmin International, Inc.
1200 E. 151st Street
Olathe, KS 66062 USA
Telephone: [phone]
Aviation Panel-Mount Technical Support Line (Toll Free) 1-888-606-5482
Dealer Line: 1-800-800-1420
Web Site Address: www.garmin.com
Garmin (Europe) Ltd.
Unit 5, Quadrangle, Abbey Park Industrial Estate
Romsey, SO51 9DL, U.K.
Telephone: [phone]
INFORMATION SUBJECT TO EXPORT CONTROL LAWS
This document may contain information which is subject to the Export Administration Regulations
(“EAR”) issued by the United States Department of Commerce (15 CFR, Chapter VII, Subchapter C) and
which may not be exported, released, or disclosed to foreign nationals inside or outside of the United States
without first obtaining an export license. A violation of the EAR may be subject to a penalty of up to 10
years imprisonment and a fine of up to US$1,000,000 under Section 2410 of the Export Administration
Act of 1979. Include this notice with any reproduced portion of this document.
RECORD OF REVISIONS
Revision Revision
Date
Description ECO #
A01/27/98 Preliminary Release -
B03/05/98 Add Music Trip Level Adjustment 8512
C02/03/99 Add Marker Sens Adjustment and Crimp Tool P/N 10404
D02/15/99 Add JTSO’s 10487
E05/28/99 Updated Document 11122
F05/26/00 Redraw 13446
G04/27/01 Add 340H P/N, STC, Mod 1 Normal/Split Com
Mode Connections, Helicopter PTT Switch
15687
H05/18/01 Added Dual ADF Version 15847
J12/18/01 Add mono/stereo failsafe note 17123
K06/24/02 Add 20 dB Music Volume Control and mod history 18443
L06/30/03 Add SB0213 and SB0221 21559

GMA 340 Installation Manual Page i
190-00149-01 Rev. L
TABLE OF CONTENTS
SECTION 1
GENERAL INFORMATION
PARAGRAPH PAGE
1.1 INTRODUCTION............................................................................................................................. 1-1
1.2 GENERAL DESCRIPTION ............................................................................................................. 1-1
1.3 SPECIFICATIONS ........................................................................................................................... 1-2
1.4 EQUIPMENT.................................................................................................................................... 1-3
1.5 INSTALLATION ACCESSORIES .................................................................................................. 1-3
1.6 ADDITIONAL EQUIPMENT REQUIRED..................................................................................... 1-4
1.7 LIMITED WARRANTY .................................................................................................................. 1-5
SECTION 2
INSTALLATION
2.1 INTRODUCTION............................................................................................................................. 2-1
2.2 UNPACKING AND INSPECTING EQUIPMENT.......................................................................... 2-1
2.3 ANTENNA INSTALLATION.......................................................................................................... 2-1
2.3.1 Location Considerations................................................................................................................. 2-1
2.3.2 Antenna Installation........................................................................................................................ 2-1
2.3.3 Antenna Cable Installation ............................................................................................................. 2-1
2.3.4 Installation Approval Considerations for Pressurized Aircraft ...................................................... 2-2
2.4 GMA 340 INSTALLATION............................................................................................................. 2-2
2.5 REAR CONNECTIONS ................................................................................................................... 2-3
2.5.1 Location.......................................................................................................................................... 2-3
2.5.2 Audio Shield Termination.............................................................................................................. 2-5
2.5.3 Noise............................................................................................................................................... 2-6
2.6 POST INSTALLATION CHECKOUT ............................................................................................ 2-6
2.6.1 Lamp Test....................................................................................................................................... 2-6
2.6.2 Failsafe Operation Check ............................................................................................................... 2-7
2.6.3 Transceiver Operational Check ...................................................................................................... 2-7
2.6.4 Intercom System (ICS) Check........................................................................................................ 2-7
2.6.5 Aircraft Receivers Check................................................................................................................ 2-8
2.6.6 Music System Check ...................................................................................................................... 2-8
2.7 ADJUSTMENTS ............................................................................................................................. 2-9

Page ii GMA 340 Installation Manual
Rev. L 190-00149-01
SECTION 3
OPERATION
PARAGRAPH PAGE
3.1 OPERATION .................................................................................................................................... 3-1
3.1.1 Front Panel Controls....................................................................................................................... 3-1
3.1.2 On, Off, and Failsafe Operation ..................................................................................................... 3-2
3.1.3 Lighting .......................................................................................................................................... 3-2
3.1.4 Transceivers ................................................................................................................................... 3-2
3.1.5 Split Com........................................................................................................................................ 3-3
3.1.6 Com Swap Function ....................................................................................................................... 3-3
3.1.7 Aircraft Radios & Navigation ........................................................................................................ 3-3
3.1.8 Speaker Output............................................................................................................................... 3-3
3.1.9 PA Function.................................................................................................................................... 3-4
3.1.10 Auxiliary Entertainment Inputs ...................................................................................................... 3-4
3.1.11 Intercom System (ICS) ................................................................................................................... 3-4
3.1.12 Mono/Stereo Headset ..................................................................................................................... 3-5
3.1.13 Marker Beacon Receiver ................................................................................................................ 3-6
APPENDIX A
CERTIFICATION DOCUMENTS
A.1 CONTINUED AIRWORTHINESS ................................................................................................. A-1
A.2 ENVIRONMENTAL QUALIFICATION FORM ........................................................................... A-4
APPENDIX B
INSTALLATION DRAWINGS
B.1 GENERAL ........................................................................................................................................B-1
APPENDIX C
STC PERMISSION
C.1 GENERAL ........................................................................................................................................C-1

GMA 340 Installation Manual Page iii
190-00149-01 Rev. L
LIST OF ILLUSTRATIONS
FIGURE PAGE
2-1 REAR CONNECTORS..................................................................................................................... 2-3
2-2 AUDIO SHIELD TERMINATION .................................................................................................. 2-5
2-3 ACCESS HOLE LOCATION........................................................................................................... 2-9
3-1 GMA 340 FRONT PANEL............................................................................................................... 3-1
B1 GMA 340 OUTLINE DRAWING ....................................................................................................B-3
B2 CONNECTOR/RACK KIT DRAWING ..........................................................................................B-5
B3 GMA 340 RECOMMENDED PANEL CUTOUT DIMENSIONS .................................................B-7
B4 J1 INTERCONNECT WIRING DIAGRAM ....................................................................................B-9
B5 J2 INTERCONNECT WIRING DIAGRAM ..................................................................................B-11
B6 J1 INTERCONNECT WIRING DIAGRAM ..................................................................................B-13
B7 J2 INTERCONNECT WIRING DIAGRAM ..................................................................................B-15
LIST OF TABLES
Table PAGE
2-1. J1 and J2 Pin Assignments ................................................................................................................ 2-4
2-2. Recommended Crimp tools ............................................................................................................... 2-5

Page iv GMA 340 Installation Manual
Rev. L 190-00149-01
GMA 340 HARDWARE MOD LEVEL HISTORY
The following table identifies hardware modification (Mod) Levels for the GMA 340 audio panel. Mod
Levels are listed with the associated service bulletin number, service bulletin date, and the purpose of the
modification. The table is current at the time of publication of this manual (see date on front cover) and is subject
to change without notice. Authorized Garmin Sales and Service Centers are encouraged to access the most up-to-
date bulletin and advisory information on the Garmin Dealer Resource web site at www.garmin.com using their
Garmin-provided user name and password.
MOD
LEVEL
SERVICE
BULLETIN
NUMBER
SERVICE
BULLETIN
DATE
PURPOSE OF MODIFICATION
1 0103 2-2-01 Configurable option to mute other com audios when
transmitting.
2 0113 6-13-01 Provides times ten gain (20 dB) for entertainment music
system.
3 0208B 5-17-02 Provides correct marker beacon output loading for interface
with a Sandel SN3308 EHSI.
4 0209 5-2-02 Provides failsafe operation when monophonic headsets are
used in a stereo installation.
5 0210 5-2-02 Provides switchable On/OFF times ten gain (20 dB) for
entertainment music system.
6 0212 7-16-02 Filter capacitors added to prevent power supply noise from
interfering with a GDL 49.
7 0213 8-26-02 Prevents current limiting resistors from becoming shorted to
the chassis.
8 0221 * Adds a failsafe warning audio to the GMA 340.
* Not released at time of publication.

GMA 340 Installation Manual Page 1-1
190-00149-01 Rev. L
SECTION 1
GENERAL INFORMATION
1.1 INTRODUCTION
This manual provides the installation and operating instructions for the Garmin GMA 340, GMA 340H and
GMA 340 Dual ADF Audio Panel. Reference to GMA 340 throughout this manual refers to all versions of the
unit. Information pertaining to the maintenance of the unit can be found in the GMA 340 Maintenance Manual,
P/N 190-00149-02. After installation of the GMA 340, FAA Form 337 must be completed by an appropriately
certificated agency to return the aircraft to service.
1.2 GENERAL DESCRIPTION
The Garmin GMA 340 Audio Panel meets the needs of aircraft owners and operators who require reliability and
versatility in the essential audio switching function. LED-illuminated push-button simplicity and intuitive panel
layout allow audio selection of both NAV and COM audio. Large, single-button activation of the COM
microphone and audio for up to three COM transceivers simplifies cockpit workload. Photocell dimming
circuitry automatically adjusts the brightness of the LEDs to a level appropriate for ambient cockpit light. A fail-
safe circuit connects the pilot’s headset and microphone directly to COM1 in the event that power is interrupted
or the unit is turned off. In the event of power loss a fail-safe warning audio will be heard.
Additionally, the GMA 340 includes a six-position intercom (ICS) with electronic cabin noise de-emphasis, two
stereo music inputs, and independent pilot, copilot, and passenger volume controls. To further simplify the
cockpit workload, the intercom provides three selectable modes of isolation. One hundred percent solid state
circuitry and extensive use of surface mount technology are employed. A pilot-selectable cabin speaker output
can be used to listen to the selected aircraft radios or to broadcast PA announcements. The PA function is pilot
selectable.
The GMA 340 is FAA TSO approved to C50c and C35d and JTSO approved to C50c and 2C35d. Also standard
is the marker beacon receiver with dual sensitivity and audio muting with automatic re-arming. 14V or 28V
operation, including the full rated range of headphone and speaker output power, is available without the
requirement for external voltage converters or dropping resistors. The GMA 340 is the standard version audio
panel as pictured on the cover of this manual. The GMA 340H is the helicopter version in which the pilot and co-
pilot control knobs on the front panel are reversed. The GMA 340 Dual ADF version, also pictured on the cover,
accepts two ADF audio inputs.
Features Summary:
•User-friendly, intuitive front panel layout
•LEDs indicate selected function
•Six position intercom: pilot, copilot, four passengers
•Three stereo headset amplifiers: one for pilot, one for copilot, and one for the passengers
•Two stereo music source inputs (one in Dual ADF version)
•Three selectable intercom operational modes
•Selectable aural pushbutton annunciation (beep) for the crew.

Page 1-2 GMA 340 Installation Manual
Rev. L 190-00149-01
•Independent pilot, copilot, and passenger volume controls
•Individual VOX circuits for each of six (6) mic inputs
•Automatic selection of radio audio source when corresponding mic is selected
•MASQTM Processing
•Split COM transceiver function. Copilot may transmit and receive on COM2 while pilot
transmits and receives on COM1
•COM swap function
•TX indication
•SmartMuteTM marker audio muting
•Speaker output for radios or PA function
•Power-off fail-safe to connect Pilot PTT, mic, and Headset to COM 1 if unit is turned off
•Power loss fail-safe warning audio
1.3 SPECIFICATIONS
SPECIFICATION CHARACTERISTIC
TSO Compliance TSO-C50c, C35d, JTSO-C50c, and JTSO-2C35d using DO-160C,
DO-170, and DO-143
Temperature Range -20°C to +55°C
Weight (Unit Only) 1.2 lbs. (0.6 kg)
(Installed with rack and connectors) 1.7 lbs. (0.8 kg)
Physical Dimensions: Bezel Height: 1.30 inches (33 mm)
Bezel Width: 6.29 inches (160 mm)
Rack Height (Dimple to Dimple): 1.33 inches (34 mm)
Rack Width: 6.30 inches (160 mm)
Depth Behind Panel with
Connectors (measured from
face of aircraft panel to rear
of connector backshells)
7.12 inches (181 mm)
Power Requirements Supply Voltage: 11.0 to 33.0 VDC; Operating Current: 2.2 A (normal
operation, 13.8 V, speaker on)
Altitude 50,000 Feet
Audio Panel Transceiver inputs: 3
Receiver inputs: 5 (6 in Dual ADF version)
Unswitched inputs: 2
Input impedance: 500ȍ(800ȍDME input in Dual ADF)
Input isolation: 60 dB minimum
Special functions: Fail-safe operation
MASQTM processing

GMA 340 Installation Manual Page 1-3
190-00149-01 Rev. L
SPECIFICATION CHARACTERISTIC
Intercom Positions: 6 (pilot, copilot, 4 passengers)
Volume controls: 3 (pilot, copilot, passengers)
VOX level controls: 2 (pilot, copilot/passengers)
VOX circuits: 6 (one per mic input)
Music inputs (stereo): 2 (1 in Dual ADF version) (one input mutable)
Music input impedance: 460 ohms minimum
Music input level: Less than 500 mVac RMS for full output (typical).
1 Vac RMS MAX (3 Vac p-p)
Microphone signal processing: 9 pole characteristic and special cabin
noise band de-emphasis
Intercom isolation modes: 3
Special functions: Configurable aural push-button annunciation for
the crew
Headphone Outputs Output amplifiers: 3, stereo (pilot, copilot, passengers)
Fidelity: Power into 150ȍDistortion
50 mW <0.5%
100 mW <5%
Frequency response: music; 100 Hz to 15 kHz nominal
Aircraft radio: 100 Hz to 6 kHz nominal
ICS mic: (Special cabin noise band de-emphasis)
Speaker Outputs Outputs selectable: 1, pilot selectable
Output power: 10 Watts into 4 or 8ȍ, @ any normal supply voltage.
Frequency response: 350 Hz to 6 kHz nominal
Special functions: PA Mode, pilot selectable, including split operation
Marker Beacon Receiver Frequency: Crystal controlled at 75 MHz
Sensitivity: LO 1000 µV hard; HI 200 µV hard
Selectivity: 6 dB @ ±10 kHz min, 40 dB @ ±200 kHz max.
Input impedance: 50ȍ
External lamp drive: 125 mA max each output
Other outputs: Middle MKR sense
Special functions: SmartMuteTM marker audio muting
1.4 EQUIPMENT
GMA 340 Audio Panel, Ship Level Assembly, P/N 010-00152-( ) includes the following, depending on part
number:
•011-00401-( )GMA 340 Unit Assembly (011-00401-10 replaces 011-00401-00)
•011-00652-00Connector Kit, GMA 340
•011-00678-00Rack Backplate, GMA 340
•115-00262-00SMP, Install Rack, GMA 340
(The installation kit is the same for the GMA 340, GMA 340H and GMA 340 Dual ADF)
1.5 INSTALLATION ACCESSORIES
•Marker beacon antenna kit (P/N 010-10175-00). [Note: A marker beacon antenna approved to
TSO C35( ) that has been installed to meet the requirements of this manual may be approved for
use with the GMA 340].

Page 1-4 GMA 340 Installation Manual
Rev. L 190-00149-01
1.6 ADDITIONAL EQUIPMENT REQUIRED
•Antenna sealant (use manufacturer’s instructions, install according to FAA AC 43.13-2A).
•Cables: The installer will fabricate and supply all system cables. Interconnect wiring diagrams
are detailed in Appendix B.
•Hardware: #6-32 100°flat head screw (6 ea.) and #6-32 self-locking nut (6 ea.). Hardware
required to mount the installation rack is not provided.
•Stereo headphone jacks (up to 6), microphone jacks (up to 6), 3.5mm stereo jacks (up to 2), and
insulating washers for all.

GMA 340 Installation Manual Page 1-5
190-00149-01 Rev. L
1.7 LIMITED WARRANTY
This Garmin product is warranted to be free from defects in materials or workmanship for one year from
the date of purchase. Within this period, Garmin will at its sole option, repair or replace any
components that fail in normal use. Such repairs or replacement will be made at no charge to the
customer for parts or labor, provided that the customer shall be responsible for any transportation cost.
This warranty does not cover failures due to abuse, misuse, accident or unauthorized alteration or
repairs.
THE WARRANTIES AND REMEDIES CONTAINED HEREIN ARE EXCLUSIVE AND IN LIEU
OF ALL OTHER WARRANTIES EXPRESS OR IMPLIED OR STATUTORY, INCLUDING ANY
LIABILITY ARISING UNDER ANY WARRANTY OF MERCHANTABILITY OR FITNESS FOR A
PARTICULAR PURPOSE, STATUTORY OR OTHERWISE. THIS WARRANTY GIVES YOU
SPECIFIC LEGAL RIGHTS, WHICH MAY VARY FROM STATE TO STATE.
IN NO EVENT SHALL GARMIN BE LIABLE FOR ANY INCIDENTAL, SPECIAL, INDIRECT OR
CONSEQUENTIAL DAMAGES, WHETHER RESULTING FROM THE USE, MISUSE, OR
INABILITY TO USE THIS PRODUCT OR FROM DEFECTS IN THE PRODUCT. Some states do
not allow the exclusion of incidental or consequential damages, so the above limitations may not apply
to you.
Garmin retains the exclusive right to repair or replace the unit or software or offer a full refund of the
purchase price at its sole discretion. SUCH REMEDY SHALL BE YOUR SOLE AND EXCLUSIVE
REMEDY FOR ANY BREACH OF WARRANTY.
To obtain warranty service, contact your local Garmin Authorized Service Center. For assistance in
locating a Service Center near you, call Garmin Customer Service at one of the numbers shown below.
Products sold through online auctions are not eligible for rebates or other special offers from Garmin.
Online auction confirmations are not accepted for warranty verification. To obtain warranty service, an
original or copy of the sales receipt from the original retailer is required. Garmin will not replace
missing components from any package purchased through an online auction.
Garmin International, Inc. Garmin (Europe) Ltd.
1200 East 151st Street Unit 5, The Quadrangle, Abbey Park Industrial Estate
Olathe, Kansas 66062, U.S.A. Romsey, SO51 9DL, U.K.
Phone: [phone] Phone: [phone]
FAX: [phone] FAX: [phone]

Page 1-6 GMA 340 Installation Manual
Rev. L 190-00149-01
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GMA 340 Installation Manual Page 2-1
190-00149-01 Rev. L
SECTION 2
INSTALLATION
2.1 INTRODUCTION
This section provides the necessary information for the installation and checkout of the GMA 340 Audio Panel.
Installation of the GMA 340 will differ according to equipment location and other factors. Cabling will be
fabricated by the installing agency to fit these various requirements. Appendix B contains interconnect wiring
diagrams, mounting dimensions, and information pertaining to installation. Each installation shall be
accomplished to meet the requirements of FAA AC 43.13-2A.
2.2 UNPACKING AND INSPECTING EQUIPMENT
Carefully unpack the equipment and make a visual inspection of the unit for evidence of damage incurred during
shipment. If the unit is damaged, notify the carrier and file a claim. To justify a claim, save the original shipping
container and all packing materials. Do not return the unit to Garmin until the carrier has authorized the claim.
Retain the original shipping containers for storage. If the original containers are not available, a separate
cardboard container should be prepared that is large enough to accommodate sufficient packing material to
prevent movement.
2.3 ANTENNA INSTALLATION
2.3.1 Location Considerations
The marker beacon antenna should be mounted on a flat surface on the underside of the aircraft. Mount the
antenna so that there is a minimum of structure between it and the ground radio stations. Locate as far away as
possible from transmitter antennas.
Best results with split COM mode will be obtained when the COM 1 and COM 2 antennas are mounted on
opposite sides of the aircraft (top/bottom).
2.3.2 Antenna Installation
Install the antenna according to the antenna manufacturer’s instructions and FAA AC 43.13-2A.
2.3.3 Antenna Cable Installation
Use coax meeting the applicable aviation regulation for the marker beacon antenna cable. When routing the
cable, avoid sharp corners and route away from high current wiring, fluorescent lighting, and any transmitter
antenna cables. Follow accepted industry practices when installing the BNC connector at the antenna end of the
cable. Use a BNC connector suitable for the type of cable used.

Page 2-2 GMA 340 Installation Manual
Rev. L 190-00149-01
2.3.4 Installation Approval Considerations for Pressurized Aircraft
Antenna and cable installations on pressurized cabin aircraft require FAA approved installation design and
engineering substantiation data whenever such installations incorporate alteration (penetration) of the cabin
pressure vessel by connector holes and/or mounting arrangements.
For needed engineering support pertaining to the design and approval of such pressurized aircraft antenna
installations, it is recommended that the installer proceed according to any of the following listed alternatives:
1. Obtain approved antenna installation design data from the aircraft manufacturer.
2. Obtain an FAA approved Supplemental Type Certificate (STC) pertaining to and valid for the subject
antenna installation.
3. Contact the FAA Aircraft Certification Office in the appropriate Region and request identification of FAA
Designated Engineering Representatives (DERs) who are authorized to prepare and approve the required
antenna installation engineering data.
4. Obtain FAA Advisory Circular AC-183C and select (and contact) a DER from the roster of individuals
identified there under.
Contact an aviation industry organization such as the Aircraft Electronics Association and request their assistance.
2.4 GMA 340 INSTALLATION
NOTE
Avoid installing the unit near heat sources. If this is not possible, insure that
additional cooling is provided. Allow adequate space for installation of cables
and connectors. The installer will supply and fabricate all of the cables. All
wiring must be in accordance with FAA AC 43.13-2A.
1. Assemble the connector/rack kit according to table 2-1 and figures B4 through B7. Install the rack
assembly according to the dimensions given in figures B1 and B3. Mounting brackets are not supplied
due to the wide range of mounting configurations available. Suitable mounting brackets may be
fabricated from sheet metal or angle stock. To insure a sturdy mount, rear support for the unit should be
provided.
2. Slide the unit into the rack until the jack screw makes contact with the receptacle located in the back
plate.
3. Insert a 3/32” Allen wrench into the jackscrew access hole on the faceplate.
4. Turn the Allen wrench clockwise until the unit is secured in the rack. Continue turning until tight, but do
not over-tighten.
5. To remove the unit from the rack, turn the Allen wrench counterclockwise until it disengages from the
rack.

GMA 340 Installation Manual Page 2-3
190-00149-01 Rev. L
2.5 REAR CONNECTIONS
2.5.1 Location
The GMA 340 has two 44 pin connectors located at the rear of the unit, designated J1 and J2. J1 and J2 pin
assignments are given in table 2-1. When viewed from the back of the rack, J1 and J2 look like the following:
Figure 2-1. Rear Connectors
NOTES
These notes apply to the following table:
* Denotes Active Low. (Ground to activate). Refer to Figures B4 through B7 for
GMA 340 interconnect wiring diagrams.
** The GMA 340 provides inputs for an unswitched aircraft radio (TEL
RINGER) and an un-muted, unswitched aircraft radio (ALT WRN).
J2 J1

Page 2-4 GMA 340 Installation Manual
Rev. L 190-00149-01
Pin # Connector J1 Connector J2
1 Mkr Ant Pilot Headset Return
2 Mkr Ant Return Co-Pilot Headset Return
3 Com 3 In Co-Pilot Headset L
4 Com 3 Return Co-Pilot Headset R
5 Com 3 Mic 14V Lgt Lo/28V Lgt Lo
6 Com 3 Key* 14V Lgt/28V Lgt Lo
7 ADF In (ADF 2 In) 14V Lgt/28V Lgt
8 ADF Return (ADF 2 Return) Aircraft Power
9 Com 1 In Aircraft Power
10 Com 1 Return Aircraft Ground
11 Com 1 Mic Aircraft Ground
12 Com 1 Key* PA Mute*
13 Com 2 In ICS Mute Inhibit*
14 Com 2 Return ICS Mute Inhibit Return
15 Com 2 Mic High Music Gain Select*
16 MASQ Inh* Pilot Headset L
17 Nav 1 In 8 Ohm Select*
18 Nav 1 Return Reserved
19 Nav 2 In Tone Enable*
20 Nav 2 Return Swap*
21 DME In (ADF 1 In) Swap Return
22 DME Return (ADF 1 Return) NC
23 Com 3 Spkr Load Music 1 L In
24 Com 3 Spkr Load Return Music 1 R In
25 Com 1 Spkr Load Music 1 Return
26 Com 1 Spkr Load Return Music 2 L In (NC)
27 Com 2 Spkr Load Music 2 R In (DME In)
28 Com 2 Spkr Load Return Music 2 Return (DME Return)
29 NC FAILSAFE_WARN
30 Com 2 Key* Com TX Mute*
31** Alt Wrn In Pilot Headset R
32** Alt Wrn Return Co-Pilot Mic In
33 Pilot Mic In Co-Pilot Mic Key*
34 Pilot Mic Key* Co-Pilot Mic Return
35 Pilot Mic Return Pass 1 Mic
36 Ext White Lamp; A Pass 1 Mic Return
37 Ext Blue Lamp; O Pass 2 Mic
38 Ext Amber Lamp; M Pass 2 Mic Return
39 Middle Mkr Sens Pass 3 Mic
40 Pass Headset L Pass 3 Mic Return

GMA 340 Installation Manual Page 2-5
190-00149-01 Rev. L
41 Pass Headset R Pass 4 Mic
42 Pass Headset Return Pass 4 Mic Return
43** Tel Ringer Return Spkr Return
44** Tel Ringer In Spkr Out
Table 2-1. J1 and J2 Pin Assignments (Dual ADF in Parentheses)
Connector Type High Density
Wire Gauge 22-28 AWG
Hand Crimping Tool Positioner Insertion/
Extraction Tool
Military P/N M22520/2-01 M22520/2-09 M81969/1-04
Positronic 9507 9502-3 M81969/1-04
ITT Cannon 995-0001-584 995-0001-739 N/A
AMP 601966-1 601966-6 91067-1
Daniels AFM8 K42 M24308/18-1
Astro 615717 615725 M81969/1-04
Table 2-2. Recommended Crimp Tools
NOTE
Non-Garmin part numbers shown are not maintained by Garmin and consequently
are subject to change without notice.
2.5.2 Audio Shield Termination
The audio shield wires should be terminated at the rear of the unit to the screws between J1 and J2 as shown in
figure 2-2.
Audio shields daisy chained and
terminated using a lug attached to
either of these screws.
Rear View of backplate and rack
340 P1340 P2
Figure 2-2. Audio Shield Termination

Page 2-6 GMA 340 Installation Manual
Rev. L 190-00149-01
2.5.3 Noise
Because the audio panel is a point in the aircraft where signals from many pieces of equipment are brought
together, care must be taken to minimize effects from coupled interference and ground loops.
Coupled interference can sneak into audio system interconnecting cables when they are routed near large AC
electric fields, AC voltage sources, and pulse equipment (strobes, spark plugs, magnetos, EL displays, CRTs, etc).
Interference can also couple into audio system interconnecting cables by magnetic induction when they are routed
near large AC current-carrying conductors or switched DC equipment (heaters, solenoids, fans, autopilot servos,
etc).
Ground loops are created when there is more than one path in which return currents can flow, or when signal
returns share the same path as large currents from other equipment. These large currents create differences in
ground potential between the various equipment operating in the aircraft. These differences in potential can
produce an additive effect at an audio panel signal input.
The audio panel may “see” the desired input signal plus an unwanted component injected by ground differentials,
a common cause of alternator-related noise. This is the main reason why all audio jacks should be isolated from
ground. Terminating audio shields just at one end eliminates another potential ground loop injection point.
Single-point grounding cannot be overstressed for the various avionics producing and processing audio signals.
Single-point, in this context, means that the various pieces of equipment share a single common ground
connection back to the airframe. Good aircraft electrical/charging system ground bonding is also important.
The wiring diagrams and accompanying notes in this manual should be followed closely to minimize noise
effects.
2.6 POST INSTALLATION CHECKOUT
CAUTION
Check wiring connections for errors before inserting the GMA 340 into the tray.
Incorrect wiring could cause internal component damage.
Except for marker beacon operation, an in-aircraft checkout may be performed in the aircraft on the ramp with
known good microphone, headset, speaker and avionics receivers. Item numbers in parentheses refer to front
panel controls shown in figure 3-1, page 3-1.
2.6.1 Lamp Test
Apply power to the unit by rotating the pilot intercom knob (5) clockwise.
The GMA 340 test button (17) checks the internal LED annunciators and marker beacon LEDs (1). Press TEST
to confirm operation of the LEDs. Cover the photocell (19) with a finger and observe that the LED annunciators
dim automatically. Check the front panel backlighting and dimming function. Each annunciation is illuminated.

GMA 340 Installation Manual Page 2-7
190-00149-01 Rev. L
2.6.2 Failsafe Operation Check
1. Turn the unit off by rotating the pilot intercom knob (5) counter clockwise.
2. Check the failsafe operation by exercising the COM 1 microphone, microphone key and audio over the
headphones.
NOTE
For units without Mod 4 incorporated, if a monaural headset is plugged into a stereo
jack the ring conductor will be shorted to the barrel conductor when the headset is
plugged in preventing proper failsafe operation. No audio will be heard. In this type of
installation, either a stereo/mono switch must be installed for proper operation or Mod
4 must be incorporated. If Mod 4 is incorporated, the audio will be heard only in the
left channel of a stereo installation. See note 13 in figures B5 and B7 and refer to
Garmin Service Bulletin 0209.
3. Turn the unit back on to continue testing.
2.6.3 Transceiver Operational Check
1. Perform a ramp test radio check by exercising the installed transceivers, microphone, microphone key and
audio over the headphones and speaker.
2. Verify that communications are loud and clear and PTT operation is correct.
2.6.4 Intercom System (ICS) Check
NOTE
If a monaural headset is used in one position, no damage will occur if plugging
into a stereo jack. In the case of passenger positions, any stereo listener will lose
one channel when another passenger plugs in a mono headset.
1. Set the intercom to the ALL mode [Crew (9) and Pilot (10) LEDs off.]
2. Plug in headsets at each ICS position.
NOTE
For helicopter operation using a two-stage Intercom/PTT switch, prior to using
the keyed-intercom mode, the VOX level should be set by adjusting the VOX
knob while the first detent is actuated and held.
3. Adjust squelch (8) and volume (7) for each position and verify that the ICS is working properly.
4. Check Pilot and Copilot ICS positions for isolation and proper operation of volume and squelch controls
(5, 6, 7 and 8).
5. Press the PA button (11). Verify that microphone audio is heard over the speaker.

Page 2-8 GMA 340 Installation Manual
Rev. L 190-00149-01
2.6.5 Aircraft Receivers Check
1. Select the audio source corresponding to each installed avionics unit and check for audio over the
headsets.
2. Check for Pilot/Copilot audio isolation when pressing the COM 1/2 button (15). (Not applicable to Dual
ADF)
3. Press the SPKR button (12) and verify that any selected audio is heard over the speaker.
2.6.6 Music System Check
NOTE
Unit Mods 2 and 5 provide times ten gain for volume control of the entertainment
music system. Unit Mod 5 provides either switching this function between unity gain
(0 dB) and times ten gain (20 dB) or hard wiring J2 pin 15 to ground for times ten gain.
When audio levels applied to Music 1 and Music 2 inputs are increased by 20 dB, the
amplification may also increase unwanted audio noise. See note 17 in figures B5 and
B7 and refer to Garmin Service Bulletins 0113 and 0210.
1. Set the intercom to the ALL mode [Crew (9) and Pilot (10) LEDs off.]
2. Connect a stereo audio source to MUSIC 1. Verify that stereo audio is heard over all headset positions.
3. Select an audio source to COM 1 (13) and verify that the sound is muted by active Com 1 audio (break
squelch if necessary).
4. Connect a stereo music source to MUSIC 2. (NA to Dual ADF). Press the CREW button (9) to set the
ICS to the crew mode. Verify that stereo audio is heard in the passenger headsets only.
CAUTION
Be sure to check all aircraft control movements before flight is attempted to
insure that the wiring harness does not touch any moving part. Verify proper
operation of the marker beacon during a flight test under VFR conditions.
This completes the in-aircraft post installation checkout. Perform a flight test after installing the unit to ensure
satisfactory performance of the audio and marker beacon receiver functions. Verify proper operation of the
marker lamps and marker audio, including the marker audio mute function. Check proper operation of the
sensitivity selection [using the SENS button (4)] by flying towards the outer marker position initially using HI
sensitivity. When the COM audio is just barely audible in the headset, switching to LO sensitivity should reduce
or eliminate the audio.